1. Field of the Invention
The present invention relates to a method for manufacturing an organic EL (electroluminescence) device and more particularly to the method for manufacturing the organic EL device that can prevent an occurrence of a leakage current caused by heat in an encapsulation process.
The present application claims priority of Japanese Patent Application No.2000-316419 filed on Oct. 17, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
As one type of EL devices to be used in a display device for information devices or a like, an organic EL device is developed. FIG. 10 is a schematic diagram showing configurations of a conventional organic EL device. The conventional organic EL device, as shown in FIG. 10, includes a transparent insulating substrate 51 made of a glass substrate or a like, an anode 52 (lower electrode) formed on the transparent insulating substrate 51 and made of transparent conductive materials such as ITO (Indium Tin Oxide), a hole transporting layer 53 formed on the anode 52, an organic light emitting layer 54 formed on the hole transporting layer 53, a cathode 55 (upper electrode) formed on the organic light emitting layer 54 and made of MgAg (magnesium silver) and a cap 57 made of glass or a like and mounted via a resin for encapsulation 56_on the transparent insulating substrate 51 on which main components including the anode 52, hole transporting layer 53, organic light emitting layer 54, and cathode 55 are formed, in a manner so as to cover the main components.
As the above resin for encapsulation 56, for example, a UV (Ultra-Violet ray curable resin is used and by irradiating the resin for encapsulation 56 with light containing UV fed from a light source, the resin for encapsulation 56 is cured and is used for encapsulation. At this point, in addition to the UV, heat is emitted from the light source and the emitted heat is further added to the main components of the EL device and, as a result, its temperature reaches 50xc2x0 C. to 60xc2x0 C. on the transparent insulating substrate 51. Moreover, since it is impossible to completely cure the resin for encapsulation 56 only by applying the UV to the resin for encapsulation 56, after the irradiation with the UV, heat with a temperature of 40xc2x0 C. to 60xc2x0 C. is added for about a half day to perform after-curing processing.
However, due to heat existing on the transparent insulating substrate 51 in the encapsulation process and heat produced by the after-curing process, a defect occurring on an interface of the organic light emitting layer 54 and the cathode 55 in an unstable state is increased. The occurrence of the defect means that an impurity level caused by a lattice defect or a like is formed in a region where an interface level is to be formed. The existence of the defect causes a path other than that through which a carrier flows originally to be produced and occurrence of the leakage current to be increased. Moreover, there is a danger that the cathode 55 is shorted to the anode 52. As a result, a characteristic of the organic EL device becomes unstable, causing an increase of defects. Moreover, since the UV light causes the increase in defects existing on the interface, when the UV light is applied, considerations are given to avoid application of the UV light to the main components of the organic EL device. Therefore, to stabilize characteristics of the organic EL device by preventing the occurrence of the leakage current caused by heat in the encapsulation process, it is desirous to remove the defects before being encapsulated.
In the manufacturing of each of various electronic components, in order to achieve stable characteristics of the organic EL device, generally, aging processing is performed. For example, a semiconductor aging apparatus used in a test for an EPROM (Electrically Programmable Read Only Memory) is disclosed in Japanese Laid-open Patent Application No. Hei 1-191075. The semiconductor aging apparatus, as shown in FIG. 11, is so constructed that the aging is performed by applying light with wavelengths of more than 400 nm from a mercury lamp 63 attached outside a thermostatic storage oven 61 through an optical filter 64 to an EPROM substrate 62 mounted in the thermostatic storage oven 61 maintained at temperatures of 200xc2x0 C. to 300xc2x0 C. This causes an electron existing in a floating gate to be excited and the excited electron to be discharged beyond a barrier, thus improving a storage characteristic of the organic EL device.
A method of aging of an EL display adapted to stabilize light emission luminance of an EL display panel is disclosed in, for example, Japanese Laid-open Patent Application No. Hei 4-79193.
In the disclosed aging method of the EL display panel, as shown in FIG. 12, when the aging is performed, since the organic EL device has many cells (each of them has both the_electrodes 72 and 73), all the electrodes 72 and 73 are commonly connected, that is, one electrode 72 (for example, cathode) and the other electrode 73 (for example, anode) are commonly connected to the EL display panel 71 and a display voltage 74 fed from an alternating power source is applied between both the electrodes 72 and 73 to emit light and, at a same time, light having energy of more than 0.3 kW is applied to only a side of the EL display panel 71 from an aging light source 75 using a mercury lamp or a like. Thus, by combining irradiation of light and application of voltages, the aging is accelerated and time required for the aging is shortened.
However, the conventional aging processing disclosed above, since it is not intended to be used for aging of the organic EL device, has the following problems.
First, since the semiconductor aging processing disclosed in Japanese Laid-open Patent Application Hei 1-191075 is intended to be used for the EPROM being one of types of the semiconductor devices, it naturally uses the thermostatic storage oven 61 with its temperatures being maintained at 200xc2x0 C. to 300xc2x0 C. However, since the organic EL device has the organic light emitting layer 54 and is vulnerable to heat, it is not proper to use the above aging method for the organic EL device. That is, though, in the case of the organic EL device, the aging has to be preferably performed at ordinary temperatures, if the aging processing disclosed above is employed, as a result, the aging is performed at high temperature, which causes problems associated with heat, as described above. Moreover, since the aging processing disclosed above is intended to be applied to a test of the EPROM for screening, no consideration has been given to improvement of device characteristics by, for example, preventing the occurrence of the leakage current caused by heat in the encapsulation process, which presents a problem.
Next, in the aging processing disclosed in Japanese Laid-open Patent Application No. Hei 4-79193, display voltage fed from the alternating power source is applied between both the electrodes and, at the same time, the light using the mercury lamp is applied to the EL display panel. However, since the light energy used for the irradiation is as large as more than 0.3 kW, if it is employed in the aging for the organic EL device, the organic light emitting layer 54 degrades. Moreover, the application of the voltage is essential in the disclosed aging processing, however, since, in the manufacturing method of the organic EL device, almost all the processes have to be performed in an atmosphere of inert gas in order to prevent the degradation of the organic light emitting layer 54, the application of the voltage is impossible. In the aging processing disclosed in Japanese Laid-open Patent Application No. Hei 4-79193, since the aging is performed in order to achieve stabilization of light emission luminance, no consideration has been given to the improvement of device characteristics by, for example, preventing the occurrence of the leakage current caused by heat in the encapsulation process, as in the case of the aging processing disclosed in Japanese Laid-open Patent Application No. Hei 1-191075.
In view of the above, it is an object of the present invention to provide a method for manufacturing an organic EL device which is capable of preventing an occurrence of a leakage current caused by heat in an encapsulation process.
According to a first aspect of the present invention, there is provided a method for manufacturing an organic EL device for performing encapsulation by using a cap, after having formed its main components by sequentially stacking a first electrode, an organic layer containing at least an organic light emitting layer and a second electrode on a transparent insulating substrate, including:
a step of applying, before performing the encapsulation, light with a wavelength of a range of 300 nm to 500 nm to a displaying surface of the transparent insulating substrate on which the main components are formed.
In the foregoing, a preferable mode is one wherein the light is applied in light quantity of a range of 0.1 to 1000 xcexcW/cm2.
Also, a preferable mode is one wherein the light is applied during irradiation time of a range of 1 min. to 30 min.
Also, a preferable mode is one wherein the light is applied in an atmosphere containing oxygen.
According to a second aspect of the present invention, there is provided a method for manufacturing an organic EL device for performing encapsulation using a cap after having formed its main components on a transparent insulating substrate, the method including:
a process of forming, after having formed a transparent conductive film on the transparent insulating substrate, an anode by performing patterning so that the transparent conductive film has a desired shape;
a process of forming, after having put the transparent insulating substrate into a deposition apparatus having at least a light emitting material, an organic layer containing at least an organic light emitting layer on the anode;
a process of forming, after having formed the organic layer, a cathode on the organic layer;
a process of placing the transparent insulating substrate in a light irradiating apparatus and then applying light with a wavelength of 300 nm to 500 nm;
a process of applying light with a wavelength of 300 nm to 500 nm wherein light quantity is in a range of 0.1 to 1000 xcexcW/cm2;
a process of applying light with a wavelength of 300 nm to 500 nm wherein irradiation time is in a range of 1 min. to 30 min.; and
a process of having the cap adhered on the transparent insulating substrate for encapsulation.
In the foregoing, a preferable mode is one wherein the light is applied in an atmosphere containing oxygen.
Also, a preferable mode is one wherein a vacuum evaporation apparatus is used as the deposition apparatus.
Also, a preferable mode is one wherein the light is applied at a temperature of less than about 60xc2x0 C.
With the above configurations, optical annealing is performed, before being encapsulated, by applying light with the irradiation wavelength xcex within a range of 300 nm to 500 nm to the transparent insulating substrate on which main components are formed and therefore interface between the organic film and cathode can be made stable. As a result, occurrence of leakage current caused by heat in an encapsulation process can be prevented.